From: "J. Bruce Fields" Subject: Re: [NFS] Does "sync" cause the FUA bit to be set? Date: Tue, 10 Jun 2008 15:47:12 -0400 Message-ID: <20080610194712.GP20184@fieldses.org> References: <484E5AC1.3020200@bio.ifi.lmu.de> <484EA146.8070201@gmail.com> <484EA215.5090000@panasas.com> <484ECD58.8040100@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Cc: Benny Halevy , Frank Steiner , nfs@lists.sourceforge.net To: Wendy Cheng Return-path: Received: from neil.brown.name ([220.233.11.133]:43359 "EHLO neil.brown.name" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754437AbYFJTrc (ORCPT ); Tue, 10 Jun 2008 15:47:32 -0400 Received: from brown by neil.brown.name with local (Exim 4.63) (envelope-from ) id 1K69oY-0004uU-B0 for linux-nfs@vger.kernel.org; Wed, 11 Jun 2008 05:47:30 +1000 In-Reply-To: <484ECD58.8040100@gmail.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, Jun 10, 2008 at 01:52:08PM -0500, Wendy Cheng wrote: > Benny Halevy wrote: > > On Jun. 10, 2008, 18:44 +0300, Wendy Cheng wrote: > > > >> Frank Steiner wrote: > >> > >>> With the profile ignoring the FUA bit, copying or deleting directories > >>> of e.g. 10M with a about 1000 files is factor 5 faster than with the > >>> profile honoring the FUA bit. > >>> > >>> > >> FUA bit is normally combined with write-thru scsi command that bypasses > >> storage write cache. I would imagine it needs to well synchronize > >> various pieces before issuing this command. It could hurt the > >> performance if not done well, particularly for meta data. So your result > >> is not surprising. > >> > >>> We export with the "sync" option. Does that option maybe set the FUA bit > >>> for all write operations on the NFS server? > >>> > >>> > >> It depends on how the filesystem (and its associated disk subsystem) is > >> implemented. The "sync" export option itself has a heavy performance > >> impact, regardless how FUA bit is handled. Some vendors uses specialized > >> HW (e.g. NVRAM) to alleviate this performance hit. If your filesystem > >> doesn't have this type of support, you should expect "sync" option runs > >> much much slower than "async". It is a choice (or balance) between cost, > >> performance, and data reliability. > >> > > > > Wendy, I *think* what you have in mind is the sync mount option > > rather than the sync export flag. The latter just tells the server > > not to cheat and do everything asynchronously. It should *not* > > have a heavy performance penalty for I/O intensive writes if the > > client is using async writes and commits. > > > > > No, I didn't get confused ... We can use Linux as an example :) .. check > out: > http://marc.info/?l=linux-nfs&m=119618886105337&w=2 > > -- quote > > The default export might have been "async", but unless the option "sync" > in /etc/exports was being ignored I was already using "sync". Nevertheless > I will try to change to async and test if it makes a difference. > > (one day later: ) > > I have now tried it and the load on the NFS server is much lower and KDE > logins seem to be reasonably fast now. Yeah, the "async" export options is expected to improve performance on a workload like that (with lots of directory creates/deletes). But it does so by violating the promises that the protocol makes to the client. --b. ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://sourceforge.net/services/buy/index.php _______________________________________________ NFS maillist - NFS@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/nfs _______________________________________________ Please note that nfs@lists.sourceforge.net is being discontinued. Please subscribe to linux-nfs@vger.kernel.org instead. http://vger.kernel.org/vger-lists.html#linux-nfs